Mobile Global Positioning System (GPS) applications and the underlying hardware solutions provide an end user the ability to work anywhere anytime, while providing a level of accuracy appropriate for Location Based Service (LBS) applications which actively require location information. For LBS applications, Time To First Fix (TTFF) is an important criterion for customer satisfaction and commercial adoption of LBS applications. For example, a consumer is likely to abandon a location based service request if the consumer has to wait for more than ten seconds to obtain satellite signals and navigation data.
When a GPS receiver is first turned on, or if the GPS receiver has not actively been receiving ephemeris information from GPS Satellites for an extended period, TTFF may take several minutes to achieve a fix, and in some instances, may not achieve a fix at all. To reduce the wait time, some LBS vendors use a control channel based protocol referred to as Radio Resource Location Protocol (RRLP), which can send the most current ephemeris File (e.g., 1667-byte four-hour-interval file) for a one time assist. Other LBS vendors also have created similar ephemeris files that provide Almanac-like data for 3 to 7 days into the future.
However, given the nature of the orbital and timing uncertainties, which often require the prediction of exactly where the active Pseudo Random Number (PRN) sources (i.e., satellites) will be with respective to their orbital positions above the earth (e.g., during each specific four-hour interval), the calculations as provided by these ephemeris files are generally not reliable.